1. Field of the Invention
The present invention relates generally to detecting and controlling electrical arcs, and specifically to detecting and controlling electrical arcs occurring in a cleaning cell of an electronic air cleaner.
2. Description of Related Art
Electronic air cleaners are currently available that filter particles from the air by charging the particles so that they have an electrostatic charge, and then passing the charged particles between high voltage plates. The plates have an electric potential between them, and the charged particles are attracted to and collected on the plate that has a polarity opposite to the charge on the particles. Thus, the particles are removed from the air. For example, if the particles are given a positive charge and then passed between two plates that have an electric potential between them, the particles will be attracted to the plate that is connected to the lesser voltage.
Arcing can occur when accumulated debris narrows an effective gap between the high voltage plates. Since the electric potential between the plates is typically large, for example at least several thousand volts, when the effective gap becomes small an arc will occur along a path across the gap. Current flows between the plates along the path, generating a high rate of change in current flow, i.e., a large dI/dt. The large dI/dt creates a burst of electromagnetic noise that often has frequency components in the 300 kHz range, a short duration on the order of several microseconds or less, and a relatively high local intensity in comparison to other electromagnetic signal sources when measured near the arc. This electromagnetic noise burst often interferes with the electronics within the air cleaner as well as with other electrical devices near the air cleaner, such as television sets, radios, and personal computers. The burst of electromagnetic noise resulting from the arcing affects digital circuits and microprocessors, because the conductive components in the circuit and microprocessors act as antennae that receive the noise signal and generate erroneous pulses. These erroneous pulses cause the digital circuits and microprocessors to reset or malfunction in unpredictable ways.
In addition, sound created by arcing in an electronic air cleaner can be especially annoying to a user because arcs typically occur in rapid succession. The arc ionizes the air in the immediate vicinity of arc's path, which increases the conductivity of the path and therefore the likelihood that subsequent arcs will occur. Where the arcing is caused by large debris trapped between cell plates in the air cleaner, arcing can continue indefinitely until the debris either burns away or falls from between the cell plates, or until a user disconnects the air cleaner's power source.
Arcing can also be undesirable for other reasons. For example, arcing generates ozone which can be harmful. Arcing can also overload the air cleaner power supply as well as consume unnecessary amounts of electrical power.